Relationship of emphysema and airway disease assessed by CT to exercise capacity in COPD

SummaryObjectiveTo assess the association of emphysema and airway disease assessed by volumetric computed tomography (CT) with exercise capacity in subjects with chronic obstructive pulmonary disease (COPD).MethodsWe studied 93 subjects with COPD (Forced Expiratory Volume in 1 s [FEV1] %predicted mean ± SD 57.1 ± 24.3%, female gender = 40) enrolled in the Lung Tissue Research Consortium. Emphysema was defined as percentage of low attenuation areas less than a threshold of −950 Hounsfield units (%LAA-950) on CT scan. The wall area percentage (WA%) of the 3rd to 6th generations of the apical bronchus of right upper lobe (RB1) were analyzed. The 6-min walk distance (6MWD) test was used as a measure of exercise capacity.ResultsThe 6MWD was inversely associated with %LAA-950 (r = −0.53, p < 0.0001) and with the WA% of 6th generation of RB1 only (r = −0.28, p = 0.009). In a multivariate regression model including CT indices of emphysema and airway disease that were adjusted for demographic and physiologic variables as well as brand of CT scanner, only the %LAA-950 remained significantly associated with exercise performance. Holding other covariates fixed, this model showed that a 10% increase of CT emphysema reduced the distance walked in 6 min 28.6 m (95% Confidence Interval = −51.2, −6.0, p = 0.01).ConclusionThese results suggest that the extent of emphysema but not airway disease measured by volumetric CT contributes independently to exercise limitation in subjects with COPD.